Safety device



Aug. 4, 1959 L. M. MOTT-SMITH SAFETY DEVICE 3 Sheets-Sheet 1 Filed April 2. 1943 T2 AT RM LEWIS M. MOT 7'- SM! BY 7/ Aug. 4, 1959 L. M. MOTT-SMITH SAFETY DEVICE 3 Sheets-Sheet 2 Filed April 2, 1943 FIG. 6

INVENTOR LE W15 M M07T$MITH 7 ATT0N% 1959 L. M. MOTT-SMITH 2,397,750

SAFETY DEVICE Filed April 2, 1943 3 Sheets-Sheet 3 FIG. 10

V I 4 9/ 89 9o 9/ 76 )v is 1' x FORWARD INVENTOR LEW/S M. MOTTSJl/TH United States Patent SAFETY DEVICE Lewis M. Mott-Smith, Houston, Tex., assignor to the United States of America as represented by the Secretary of the Navy Application April 2, 1943, Serial No. 481,643

1 Claim. (Cl. 102-84) This invention relates to safety devices for explosive projectiles of the type which. is fired from rifled guns and has particular reference to a novel clock-work safetydelay device. The new device is accurate and reliable in operation and may be made in a compact form.

It is important that the detonating device used in the fuzes of explosive projectiles be maintained in a safe condition until the projectile is at a safe distance from the gun, so that premature detonation of the projectile with consequent injury to the gun crew and damage to the gun and its emplacement may be prevented. Experience has shown that one of the most effective methods for preventing premature detonation of an explosive projectile is to block the discharge passage leading from the detonating squib, whereby the blast from the squib is prevented from reaching the usual booster if the squib should he accidentally detonated, the blocking means being automatically removed from the passage when the projectile is to be armed.

One object of the invention resides in the provision of a novel clock-Work safety-delay device for blocking the squib discharge passage until after the lapse of a predetermined period after firing of the gun, that is, until the projectile is at a safe distance from the gun. A device made in accordance with the invention comprises a squib holder having a discharge passage for communicating with a receptacle for the usual booster, and a gate normally blocking the passage and movable to an arming position by centrifugal force to unblock the passage. A pin, or the like, normally engages the gate for locking it in an unarmed position, and the pin is released under control of a clock-work mechanism having a driving element actuated by centrifugal force due to rotation of the projectile. The clock-work mechanism is normally locked against operation by means which responds to centrifugal force or a force of setback, or both, to release the mechanism when the projectile is fired. In the preferred construction, the detonating squib is of the electrical type and is normally shortcircuited by a wire which is broken by movement of the gate under the action of centrifugal force when the gate is released.

Another object of the invention is to provide a mechanism of the character described wherein the clock-work mechanism is normally held in an inoperative position but is rendered operative by the forces of setback during acceleration of the projectile and is operated by centrifugal force following a decrease in the forces of setback and during the flight of the projectile toward the target.

A further object of the invention is to provide a clockwork safety-delay device of relatively simple construction which occupies only a small space in the projectile casing.

These and other objects of the invention will be understood by reference to the accompanying drawings, in which Fig. 1 is a side view of a projectile embodying one form of the new safety device, with part of the casing broken away to show the device;

2,897,760 Patented Aug. 4, 1959 Fig. 2 is an enlarged axial sectional view of the safety device shown in Fig. 1;

Fig. 3 is a transverse sectional view on the line 3-3 in Fig. 2;

Fig. 4 is a transverse sectional view on the line 4-4 in Fig. 2, with parts of the device broken away;

Fig. 5 is a transverse sectional view of part of the device on the line 55 in Fig. 2;

Fig. 6 is a transverse sectional view of another part of the device;

Fig. 7 is a longitudinal sectional view of part of the device, showing the means for locking the clock-work mechanism;

Fig. 7A is a similar view showing a modified form of the lock;

Fig. 8 is a schematic perspective view of the device illustrated in Fig. 2, showing a detonating circuit under control of the device;

Fig. 9 is a transverse sectional view of a modified form of the new safety device;

Fig. 10 is a longitudinal sectional view on the line 10 10 in Fig. 9, with parts of the device broken away, and

Fig. 11 is a schematic perspective view of the device shown in Figs. 9 and 10.

Referring to the drawings, the safety device of the present invention is shown mounted in a projectile comprising a casing 20 having the usual rotating band 21 which acts to spin the projectile by engagement of the band in the rifiing grooves of the gun barrel when the projectile is fired from the gun. The casing 20 contains a charge of high explosive 22 and a can 23 embedded in the explosive and housing a suitable fuze (not shown). At its rear end, the can 23 is internally threaded to receive the safety device 24 which contains a firing squib, to be described presently, operable by the fuze to explode the usual booster 25 for detonating the main charge 22, the booster being connected to the rear end of the safety device.

The safety device 24 comprises a cylindrical body 27 having an external flange 28 at its rear end for engagement with the corresponding end of the can 23. In front of the flange 28, the periphery of the body is provided with threads 29 adapted to mate with the threads in the can 23. The rear end portion of the body 27 has a threaded recess 30 into which the front end of the booster 25 is screwed. Intermediate its ends, the body 27 is formed with a transverse cylinder 31 terminating at one end near the periphery of the body where the cylinder is enlarged. as shown at 32. A second cylinder 33 extends transversely of the body at right angles to the cylinder 31, the two cylinders being separated by a thin frangible wall 34 (Fig. 5). The cylinder 33 receives an electrical detonating squib 330 which, when it explodes, is designed to break the wall 34 and fire the booster through cylinder 31 and a longitudinal discharge passage 35 communicating with the booster recess 30.

The squib discharge passage 35 is normally blocked by a gate or plunger 36 slidable in the cylinder 31 and disposed between passage 35 and the frangible wall 34, whereby accidental explosion of the squib is prevented from firing the booster. The passage 35 is disposed with its axis tangent to the wall of cylinder 31 at a point op posite the wall 34 so that, in the event of a premature detonation of squib 33a, the blast from the squib will force the plunger 36 against the adjacent end of passage 35 and thereby prevent any portion of the blast from reaching the booster. At its outer end, the plunger 36 has a detent 37 in line with but normally separated from a shortcircuiting wire 38 extending diametrically across a central opening in an insulating plug 39 disposed in the enlargement 32.

On the front end of the body 27 is a casing made up of three super-imposed discs 41, 42, and 43. The disc 43, which engages the body 27, is provided in its front face with an elongated recess 44 extending diametrically across the disc, and an elongated recess 45 extending at an acute angle to the recess 44 and intersecting the latter intermediate its ends. A generally circular recess 46 is disposed on one side of the recess 44 and communicates therewith. Rotatably mounted in the recess 46 is an escapement wheel 47 having on its front face a pinion 48. the pinion and wheel being journalled at one end in the disc 43 and at the opposite end in the disc 42. The wheel 47 is controlled by a conventional escapement 50 forming part of an artillery balance lever having diametrically opposed arms 50a in recess 45, the lever, in turn, being controlled by a leaf spring 51 connected thereto and disposed in recess 44 on brackets 52. The escapement is normally locked against operation by an arm 53 pivotally mounted on the disc 43 and having a pin 54 normally engaging one of the lever arms 50a. A leaf spring 55 normally holds the arm 53 in its locking position, but when the arm is subjected to centrifugal force due to rotation of the projectile, its free end flies outwardly against the action of spring 55 to release the escapement, the arm 53 being then locked in an inoperative position by spring 55.

The pinion 48 meshes with a gear 57 rotatably mounted in a recess in disc 42 and having a pinion 58 secured to its front face, the gear and pinion being journalled at one end in the disc 42 and at the opposite end in a cover plate 59 on the front face of disc 41. A gear 60 which meshes with pinion 58 is mounted on a stud 60h journalled at its ends in the disc 42 and cover 59, the gear 60 being secured to the rear face of the hub portion of a pendulum cam 62 mounted on the stud in an arcuate recess 63 in the disc 41. The cam 62, as shown in Fig. 4, has a finger 62a extending radially from its hub portion opposite a shoulder 63a in the recess, the shoulder being normally spaced from the finger. A generally L-shaped arm 62b projects from the hub portion of the cam and is normally engaged at its free end with a shoulder 63b in the recess. A weight 64 is secured to the rear face of the arm 62b near its free end and is operable by centrifugal force to swing the cam clockwise (Fig. 4) on the stud 60a and thereby engage an arcuate shoulder 63c on the cam with the shoulder 63a. it will be understood that the finger 62a is designed to clear shouler 63a.

The rear face of finger 62a normally engages the reduced end portion of a plunger 66 extendingrearwardly through openings in the discs 42 and 43 and projecting through a passage in body 27 into the cylinder 31. The rear end of plunger 66, as shown, engages the outer end of plunger 36 adjacent the detent 37 so as to lock the plunger 36 in its inner position where it blocks the i squib discharge passage 35. Intermediate its ends, the plunger 66 has a collar 67 engaging one end of a compression spring 68 coiled around the plunger 66 and seated on the front face of body 27.

The cam 62 is normally locked in position to engage its finger 62a with the end of plunger 66, and for this purpose there is provided a plunger 70 disposed in the depression in shoulder 630 of the cam. The plunger 70 is slidable longitudinally in a passage extending through the discs 42 and 43 and terminating in the body 27, the plunger having a reduced portion at its rear end around which a compression spring 71 is coiled. One end of the spring 71 is seated on the end of the plunger passage in the body 27, and the other end of the spring is seated on the shoulder adjacent the reduced portion of plunger 70, so that the spring 71 normally urges plunger 70 forwardly to retain it in the position for locking the cam 62. A generally U-shaped spring 73 is seated in a recess 74 in the front face of the body 27, one leg of the spring 4 73 being urged against the periphery of plunger which is formed with an annular groove 75 a substantial distance in front of spring 73. The casing made up of the discs 41, 42 and 43 may be secured in any suitable manner to the body 27 and is preferably enclosed in an insulating cap 76 on the body.

If desired, a plunger of the form shown in Fig. 7A may be substituted for the plunger 70. The plunger of Fig. 7A is shown at 70a and includes a shank 70b which is counter-bored throughout its rear end portion to define a recess 70c for receiving a compression spring 70d. An annular groove 70a is formed in the shank 70b substantially medially of its length. The plunger 70a operates in a manner similar to the plunger 70. The spring 70d will, of course, urge the plunger forwardly for normally retaining the cam against rotation.

The squib 33a is designed to be fired electrically by a circuit including a battery 78 and a normally open switch 79 which may be closed automatically when the projectile is in proximity to the target, as by means of a proximity fuze. In order to prevent firing of the squib in the event that the switch 79 is closed accidentally, there is provided a shortcircuit for the squib including wires 80 connected to the ends of the wire 38 in the insulating plug 39.

The operation of the safety device is as follows:

When the projectile is fired from a gun, the resulting force of setback moves the plunger 70 rearwardly against the action of spring 71, whereupon spring 73 snaps into the groove 75 so as to lock the plunger 70 in a retracted position, with a result that the cam 62 is released. The friction between weight 64 and the bottom of recess 63 due to the initial force of setback is sutficient to prevent rotation of the cam 62 under the centrifugal force on the weight resulting from rotation of the projectile. However, when the friction is reduced by a decrease in the force of setback, the action of centrifugal force on the weight 64 rotates cam 62 clockwise (Fig. 4) on the stud 60a, the speed of rotation of the cam being controlled by the clock-work mechanism including escapement wheel 47 geared to the cam. It will be understood that on initial rotation of the projectile, the escapement locking arm 53 swings outwardly under centrifugal force to release the escapement and thereafter is held in its inoperative position by spring 55. As the cam rotates in recess 63, the plunger 66 is held by the lower face of the cam in position to lock the plunger 36 over the squib discharge passage, but when the cam approaches the end of its movement, which is limited by engagement of shoulder 630 with shoulder 63, a recess 82 in the cam moves opposite the reduced end of plunger 66. Accord ingly, the plunger 66 is then snapped forwardly under the action of spring 68 to release the plunger 36, and the latter moves outwardly in cylinder 31 under centrifugal force to unblock the squib discharge passage 35. At the same time, the detent 37 enters the central opening in plug 39 and breaks the wire 38 so as to remove the shortcircuit of squib 33a. The projectile is now armed and ready for detonation by closing of the switch 79. When the switch is closed, the squib is fired by the battery and fractures the thin wall 34 so that the booster 25 is exploded through cylinder 31 and passage 35, with the result that the projectile is detonated.

The device shown in Figs. 9, 10 and 11 comprises a cylindrical body 27a having a threaded recess 30a in its rear end for receiving the booster 25. A cylinder 310 extends transversely of the body intermediate its ends adjacent a chamber 33b for receiving a squib 33c, the cylinder and chamber being separated by a thin, frangible wall 34b which is designed to be fractured by explosion of the squib. The cylinder 31a communicates with the booster through a longitudinal discharge passage 350. A plunger 36a is slidable in cylinder 31a and has a detent 37a on its outer end disposed in line with a wire 38a which extends across a central opening in an insulating plug 39a mounted in an enlargement in the outer end of the cylinder.

On the front face of the body 27a is a casing made up of two superimposed discs 84 and 85 enclosed in an insulating cap 76a on the body. A shaft 86 extends longitudinally of the body 27a through disc 85 and is rotatable in the body, the rear end portion of the shaft 86 being normally received in a transverse groove 87 in plunger 360. A cutaway portion 88 is formed in the shaft adjacent plunger 36a, so that when the shaft is rotated approximately 90 its rear end portion is withdrawn from the groove 87 to allow movement of the plunger through the cutaway portion 88. Near its front end, the shaft is provided with a hub 86:: secured to the rear face of a semicircular gear 89. the hub having a stud 90 projecting through the axis of the gear and journalled in the disc 84. The gear 89 has an arcuate slot 91 and a weight 91a secured to its rear face so that the centrifugal force incident to the spin of the projectile causes the gear to rotate shaft 86.

The gear 89 is normally locked in a safe position by a pin 93 slidable longitudinally in disc 85 and having a head 93a, and a coiled compression spring 94 in the body 27a engages the head 93a to urge the pin forwardly in its locking position. A pinion 96 meshes with gear 89 and has an escapement wheel 97 secured to its rear face. The wheel 97 coacts with an escapement 98 form ing part of an artillery balance lever having diametrically opposed arms 98a, the lever being controlled by a leaf spring 99 disposed in a longitudinal recess 100 in disc 58 and mounted in brackets 101. The escapement is normally locked against operation by a pivoted arm 103 having a pin 104 near its free end engaging one of the lever arms 98a. The arm 103 is urged toward its locking position by a spring 105, but when the arm is subjected to centrifugal force incident to rotation of the projectile, it swings outwardly on its pivot against the spring 105 so as to release the escapement, the locking arm being held in its inoperative position by centrifugal force.

In operation, the plunger 36a is normally locked by shaft 86 in a retracted position where it blocks the squib discharge passage 35a so that accidental explosion of the squib cannot fire the booster through discharge passage 35a. When the projectile is fired from a gun, the initial force of setback moves the pin 93 rearwardly against spring 94 so as to release the gear 89 which is then rotated clockwise by the centrifugal force acting on weight 91a incident to rotation of the projectile by the gun rifiing, the speed of rotation of the gear being controlled by the clockwork mechanism including the escapement 98. The shaft 86 is rotated by gear 89 to cause the cutaway portion 88 of the shaft to move in line with plunger 36a so that the plunger is released from the shaft. After the initial force of setback is dissipated, the spring 94 will urge the pin 93 toward locking position. However, as the pin 93 will have been displaced from its opening in the disc 85, it will be canted by the effect of centrifugal force so that its upper end will be out of alinement with the disc opening. Thus, the pin 93 will be held permanently in its retracted position. The rotation of the gear 89 is limited by a stop 89a mounted on the upper surface of the disc 85. The

plunger 36a, as soon as it is released from shaft 86, moves outwardly under centrifugal force so as to unblock the squib discharge passage 35a. Outward movement of the plunger also engages the detent 37a with wire 38a and breaks the wire so as to remove the shortcircuit a of the squib, whereupon the latter may he fired electrically from battery 78a when the fuze switch 79a is closed. The explosion of the squib fractures the thin wall 34b and detonates the booster 25 through cylinder 31a and discharge passage 35a.

The new safety device is of simple construction, is positive and reliable in operation and may be made in a compact form which occupies only a small space in the projectile. The device provides dual protection in that it includes means for shortcircuiting the squib and also for blocking the explosion from the squib, if it should be accidentally fired. The clockwork mechanism affords an adequate time delay so that arming cannot take place until the projectile has travelled a safe distance from the gun. It will be evident that arming of the device results only from the combination of centrifugal force and the force of setback incident to firing the projectile.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

A safety device for use in rotary projectiles, said device comprising a housing, clock-work mechanism in said housing, said mechanism including a driving element operable by centrifugal force, a locking rod normally bearing against a portion of said element and thus being prevented from shifting but being released when the drive element has moved a predetermined amount in driving the remainder of the clock-work mechanism, an electrically operable detonating squib in the housing, the housing having a discharge passage leading from the squib, a gate normally closing said passage but movable by centrifugal force to open the latter, said gate normally being locked against such motion by the locking rod, resilient means urging the said rod away from said gate and against the driving element to cause the rod to shift after the said element has moved out of its way. and a conductor short-circuiting the squib, said conductor being located adjacent the gate and in the path of motion of the latter, whereby the conductor is mechanically disrupted by the gate upon actuation of the said gate.

References Cited in the file of this patent UNITED STATES PATENTS 1,362,519 Wilck Dec. 14, 1920 1,640,165 Varaud Aug. 23, 1927 1,665,666 Junghans Apr. 10, 1928 1,688,652 Pearson Oct. 23, 1928 2,398,439 Middlemiss Apr. 16, 1946 FOREIGN PATENTS 254,307 Italy 1927 284,968 Great Britain Feb. 9, 1928 285,553 Great Britain Feb. 16, 1928 284,186 Great Britain Jan. 26, 1928 91,592 Sweden Feb. 24, 1938 

